Adhesive



Patented June 11, 1940 UNITED STATES ADHESIVE Richard Gurley Drew,

to Minnesota St. Paul, Minn, mignor Mining & Manufacturing Company. St. Paul. Minn., a corporation of Delawllo.

No Drawing. Application February 18 1938,

Serial No. 191,268

6 Claims.

This invention relates to an adhesive or cement composition adapted to form normally tacky and pressure-sensitive adhesive coatings, and comprised of rubber and ester gum dispersed in a suitable volatile liquid vehicle.

. An object of the invention is to provide an adhesive. composition which may be applied to a wide variety of surfaces to form an adherent adhesive coating, including paper, leather, glass, and films of regenerated cellulose, cellulose esters and ethers (as cellulose acetate and ethyl cellulose), and resin films, etc. When applied to smooth impermeable surfaces, not having a special bonding action, an adhesive'coating is formed which may be stripped off. The adhesive coating formed upon evaporation of the vehicle is normally tacky and pressure-sensitive, that is, under ordinary atmospheric conditions the adhesive coating is stably in a condition such thatit does 20 not need to be activated by heat or solvents or otherwise prepared in order to exert an adhesive action.

Thus the adhesive composition may be spread upon a backing to form a stable tacky adhesive coating upon evaporation of the vehicle, permitting the backing to be pressed against a desired surface to secure immediate complete adhesion without waiting for any drying or setting action. In this case the adhesive with the backing to which it was first applied may be stripped from r the second surface without leaving a residuum of adhesive thereupon, for the adhesive coating is most firmly united to the surface to which applied in disperse form (since a more intimate con- 35, tacting is effected), and the final adhesive coating possesses greater internal cohesiveness than the adhesiveness of its surface.

A further object is to provide an adhesive composition which will iorm transparent adhesive coatings. v

In the description and claims it will be understood that I refer vto the low-acid type of ester gum (acid number generally 2 to 10). I have disa covered that this type of resin has unsuspected advantages in comparison with related types. Ii wood rosin is used, there will be a gradual development of small crystals throughout the adhesive coating, while ii gum rosin is used there will be an absence of crystallization but a more rapid aging of the rubber, and furthermore gum rosin imparts inferior color and transparency.

The use of ester gum makes for better aging and there is an entire absence of crystallization, while the color and transparency of the adhesive coatings are as good as when the best grade of wood rosin is employed. The use of ester gum makes -for greater cohesiveness (firmness) in the adhesive coating.

A further desirable characteristic of ester gum, which I have discovered, is that an adhesive made 5 therefrom may contain certain coloring pigments of a type which would catalyze oxidation of the rubber component if rosin were employed in place of ester gum. Thus my present adhesive may be colored by incorporation of gold bronzing powder 10 (powdered brass, containing copper and zinc) I! this bronzing powder were employed in a rubberrosin adhesive, the rubber would quickly age due to the strong catalytic action of the copper in the presence of rosin.

The :lollowing examples illustrate adhesive compositions prepared in accordance with my invention, all parts being by weight.

Example 1 Parts Milled latex crepe- 250 Ester gum-.. 175 "Flectol 2B (antioxidant) 1.25 Heptane (volatile solvent) 2500 25 The raw latex crepe is milled for about 10 minutes, at a temperature of about 140-150 F., and is then cut into small pieces.

The ester gum is dissolved in an equal amount of the solvent, and the Flectol B" is likewise dissolvedin a portion of the solvent. The balance of the solvent (to make a total of 2500 parts) is placed in a suitable churn and the solutions 0! ester gum and Flectol B," and the milled latex crepe, are added. The mixture is mixed until homogeneous, involving mixing for about 40 hours at a temperature of about -100" F. The resulting adhesive solution is ready for use to form, upon spreading and evaporation of the solvent, a normally tacky and pressure-sensitive transparent adhesive coating.

The indicated heptane may be substituted for by another volatile rubber solvent such as benzol or naphtha. It will be understood that the proportion of solvent may be varied to produce the desired viscosity of the adhesive composition. Thus the proportion in the above formula may be increased to make for easier brushing or spreading and a thinner coating.

For forming highly aggressive and highly cohesive adhesive coatings, the ester gum should be used in the ratio of-about 0.5-0.9 part per part of rubber. The ratio in the above formula is 0.7. To form coatings which are less tacky, but still 5| "pressure-sensitive," the ratio may be reduced to as low as 0.2, and even smaller ratios may be employed where only a comparatively slight tack isdesired. For forming highly aggressive adhesive coatings of less cohesiveness, the ratio may.

Example 2 Parts Milled latex crepe 250 Ester g I Flectol B" 1.25

Hepta 1550 Alcohol 155-31 The procedure is the same as in the preceding example.

The alcohol may be denatured ethyl alcohol (for example containing 5 volumes of methyl alcohol or ethyl acetate per 100 volumes. of proof ethyl alcohol) or may be methyl alcohol. The function 01' the alcohol is to reduce the quantity of rubber solvent required to produce a solution of desired viscosity, the alcohol being eifective even in small proportions as a viscosityreducer.

In the above examples, Flectol B (a liquid condensation product of acetone and aniline) is usedas an antioxidant to improve the rubber aging qualities. Other suitable antioxidants or age-resistors are: Flectol H (a solid condensation product of acetone and aniline), "Solux" (p hydroxy N phenylmorpholine), Agerite Resin (aldol-alpha-naphthylamine reaction product), "Antox", beta-naphthol, Agerite Alba and "Agerite White. Those which are As previously mentioned, a coloring pigment may be incorporated inthe adhesive. This may be conveniently accomplished by milling the pigment into the rubber during the preliminary milling of the latter. Thus, para toluidine red may be added to give a red color, or goldbronzing powder to give a gold color. Zinc oxide may be incorporated it desired.

What I claim is as follows:

1. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings, comprising one part raw rubber and 0.2-4 parts lowacid type ester gum dispersed in a volatile vehicle.

2. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings, comprising one part lightly milled raw rubber and 0.2-4 parts low-acid type ester gum dispersed in a volatile vehicle.

3. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings free from crystallization development, comprising one part latex rubber and 0.2-4 parts low-acid type ester gum dispersed in a volatile vehicle.

4. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings free from crystallization development, comprising one part latex rubber and 0.2-4 parts low-acid type ester gum, and a small proportion of a rubber antioxidant, dissolved in a volatile rubber solvent.

5. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings free from crystallization development, comprising one part latex rubber, 0.5-0.9 part-s low-acid type ester gum, and a small proportion of a rubber antioxidant, dissolved in a volatile rubber solvent.

6. An adhesive composition adapted to form highly coherent normally tacky and pressuresensitive transparent adhesive coatings, comprising one part raw rubber and 0.2-4 parts lowacid type ester gumdissolved in a volatile hydrocarbon rubber solvent containing a small proportion of alcohol. g

RICHARD GURLEY DREW. 

